The present invention relates generally to seals, and more particularly, to seals adapted for specialized, severe service applications.
One application for which there have been a large number of seals proposed is that of the so-called track pins on crawler tractor equipment. Crawler tractors usually include a pair of tracks, and each track is in turn made up of inner and outer chains of track links. A large plurality of links, typically 30 to 40 links, are assembled into an endless chain, and two such chains are then trained over the front idler roller and the rear sprocket final drive as well as over a number of suspension track rollers and track-carrying idler rollers. The inner and outer links in each chain are held together by track pins and bushings which extend through openings at either end of the track links. Track shoes or grouser plates extend transversely between the respective links on the inner and outer chains. These shoes or plates form the surface which rests on the earth and ultimately supports and forms the traction for the vehicle. Thus, the right and left hand vehicle tracks each include a plurality of plates, with the plates extending between and joining the links in the inboard chain to the links in the outboard chain.
Because track vehicles are particularly designed for use under severe conditions, namely, mud, sand, grit, ice and snow, rocky terrain, etc., and because the track is the portion of the vehicle which comes into the most direct and frequent contact with these severe conditions, track pins and their bushings are subject to rapid wear.
Numerous track pin seal designs have been proposed, and some of them have been proved successful in use to a certain extent; however, most crawler vehicles either use no track pin seals, or use rudimentary forms thereof, such as, for example, metal Belleville washers placed back to back, etc. Because each track contains a large number of pins, the expense of a seal is an important consideration in adopting it.
Considering the design and use environment of crawler tractors and the track links and pins and bushings thereof, an ideal track pin seal is one which will accommodate a relatively great degree of axial dimensional variation, whether such dimension occurs as a result of cumulative tolerances in manufacturing (so-called "tolerance stack up") or results from stresses and strains in use, and of course, eventual wear. As a corollary of the foregoing facts, it will be appreciated that metal Belleville washer type seals or other seals having a high axial spring rate are not highly desirable for an application of this type. An ideal track pin seal is one which has an axial spring rate which is moderate or fairly low, and yet which will generate an initial axial force which is sufficient to insure that the seal can successfully exclude water and grit and retain lube, even under conditions of minimum load. Because of the ever-increasing cost of machine parts, and the high cost of maintenance and labor, there has been and still is a great need for a really effective track pin seal. Because of user requirements generally, and more specifically, because of government and other regulations, noise reduction has recently assumed great importance and an effectively sealed and lubricated track chain is much less noisy than an unsealed, unlubricated chain.
According to the present invention, one seal which has provided excellent performance with moderate cost is described and claimed in U.S. Pat. No. 4,094,516, and the present invention is an improvement on the seal of such patent. An improved seal is provided which has most or all of the advantages of highly expensive prior art seals, which provides them at low initial cost, and which contains still further improvements over the low cost seals which incorporate such advantages. The seal of the invention applies proven principles, but uses structures and materials which are different from the prior additional structural elements in order to provide new operating characteristics and advantages.
In view of the need referred to above for an improved, highly reliable low cost seal for track pins and related applications, it is an object of the present invention to provide a novel seat for track pins and similar applications.
Another object of the invention is to provide a track pin seal having reinforcing structure adapted to improve reliability and long term life without much increase in low initial cost.
Another object of the invention is to provide a seal which utilizes a novel arrangement of an end face, an end face support, a mating surface, and axial loading member therefor.
A still further object is to provide an end face seal using two different elastomeric materials, and a reinforcing unit, the softer of which elastomer provides an axial end load application and torque transmission capability in all types of weather conditions, the harder of which elastomer provides outstanding wear resistance, and a metal or other hard reinforcing unit, with the softer element also providing a secondary or relatively static seal between itself, the harder member and the part of the track link in which it is received, and the reinforcing unit aiding performace while being incorporated into low cost form.
Another object of the invention is to provide a seal wherein the primary seal ring receives a radial compressive load from the secondary seal member, and which resists undue radial deformation by reason of having portions of such primary seal ring engage a part of the track pin itself, and in which the axial load is distributed and controlled by a stiffener or reinforcing member.
A still further object is to provide a reinforced track pin seal in which the primary seal member is supported by a portion of the track pin, and wherein the seal ring includes means permitting passage of oil from a reservoir area to the interface between the primary seal ring and the mating part.
Another object is to provide a track pin seal having three pieces and adapted to be supported by a track pin or a member associated therewith, with the so-called secondary seal member being adapted to transform an axially applied load into a combination of increased radial compressive load and a partially reduced axial load, and with the axial load applied to the primary seal face being distributed and/or controlled by a stiffener or reinforcing unit.
A further object is to provide a seal unit having three pieces, one of which comprises a primary sealing ring of a tough, but resilient elastomeric material having excellent abrasion resistance, another of which comprises a secondary seal ring made from a softer elastomer, with the second ring and a third member, a stiffener, being adapted to cooperate in applying the loading forces necessary to create an effective sealing action.
The foregoing objects and advantages of the invention are achieved in practice by providing a seal unit having a generally annular secondary seal and force applying member of a characteristic shape, a primary seal ring of a stiff, elastomeric material having a generally L-shaped seat for receiving the secondary member, and having an axially directed end face portion adapted to contact a part of the track pin mechanism to be sealed, and a reinforcing member of generally annular shape with a L-shaped cross-section, adapted to receive and distribute the forces from the secondary member so as to maintain a sealing effect and reduce primary ring distortion, with the primary seal ring including plural axial passages extending between the axial ends of the primary seal ring to permit flow of lubricant therethrough even under difficult conditions.
The exact manner in which these and other objects and advantages are achieved in practice will become more clearly apparent when reference is made to the following detailed description of the preferred embodiments of the invention set forth by way of example and shown in the accompanying drawings, in which like reference numbers indicate corresponding parts throughout.